I am one of those people who has to mess with a recipe even the very first time I make it. I just have to make it my own, and it's fun to see if I can improve on it at the same time. Love to add that 'secret ingredient' that makes something special and different, and that makes it hard to replicate unless a person has the directions.
Once I felt comfortable cooking (started making entire meals and some pretty complicated things when I was 11), I started experimenting with different combinations of foods.
Not every time, but often I can figure out how to make something just from the taste and texture of it. If there's something I really love at a restaurant, I will go home and try to replicate it so that I can have it anytime I want it instead of having to depend on the restaurant.
I don't know what it is, but I just can't leave anything in the way of recipes the way they are. My oldest sister is the same way, and she is fond of making new recipes 'her way' for the first time at dinner parties where a flub will really be noticed. So far, she's never had a flub! I'm not quite that brave myself. I would have to test a recipe before putting it on a menu for guests.
When it comes to convenience foods, like cake mixes and other types of mixes or kits for making something, I highly recommend one follow the directions to a T lest it be spoiled because all the measurements have already been done by someone else. Of course one can usually add garnishes without ruining anything, but I would't advise adding more eggs or more liquid, etc. But once I'm familiar with a mix/kit that becomes fair game too.
It can be a lot of fun to experiment with recipes. I've never had anything turn out so badly it wasn't edible. It's really a matter of being familiar with how various spices and food items taste when processed a certain way. Then you can try lots of different combinations successfully.